Remove unneeded libexif build codes

Libexif dependency is not needed now. Remove it from build.sh and jni/Android.mk

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>
Updated README file

Readme file has been updated inform of build instructions, dependencies and
usage.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>